Manholes and manhole covers are everywhere that civilization has infrastructure. They are basic to both storm sewer and sewage structure. Additionally, underground utility lines of all sorts are accessed for maintenance, repair and replacement by the use of manholes topped by metal or concrete rings or housings on which a manhole cover is mounted.
Traditionally, the weight of a manhole cover has been considered sufficient to maintain them on their mountings. However, in many parts of the world, the metal content of the manhole cover is considered worth stealing by the locals. Further, in this age of terrorism, improvised explosive devices (IED) planted by the side of a road are a main weapon of a lawless group. The positioning of manholes and their covers along roadways would provide such groups with an unwarranted convenience if the manhole covers were not locked down.
Through the years, manhole covers and their mounting rings have been generally cylindrical or rectangular in nature, with cylindrical being the preferred shape. While the design patterns of the tops of manhole covers may vary, as with vent holes, cross bars, or the like, a substantial number of manhole covers have a U-shaped access hole adjacent the outer circumference of the manhole cover in a large access hole, or about ⅞×¾ inch in a smaller access hole of a “concealed pickhole” manhole cover. These holes, due to casting, generally have a slight draft or acute angle from the horizontal, as does an inner lip of a cast manhole cover housing.
Patents that require a specially made manhole cover or rim that includes a locking apparatus include U.S. Pat. Nos. 1,473,986; 4,964,755; 5,082,392; 5,324,135; 6,199,414; and 6,854,922. Lock mechanisms that may work with standard manhole covers include U.S. Pat. Nos. 3,980,329; 6,881,007; and Publication 2007/0081856.
A need has developed for a less expensive, more generally useful manhole cover lock that is usable on existing designed manhole covers of differing general configurations.